摘要：如果為負(fù)值，表示不運行檢測線程。默認(rèn)為策略的類名，默認(rèn)為這里就用到了上面提到的兩個參數(shù)對象池原理分析避免泄漏配置參數(shù)詳解，以及資源回收，從池中獲取資源，將資源返還給池邏輯解析
序
本文主要解析一下apache common pools下的GenericObjectPool的參數(shù)設(shè)置
GenericObjectPool
commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java
public class GenericObjectPool extends BaseGenericObjectPool
implements ObjectPool, GenericObjectPoolMXBean, UsageTracking {
//......
}
默認(rèn)配置見
commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPoolConfig.java
public class GenericObjectPoolConfig extends BaseObjectPoolConfig {
/**
* The default value for the {@code maxTotal} configuration attribute.
* @see GenericObjectPool#getMaxTotal()
*/
public static final int DEFAULT_MAX_TOTAL = 8;
/**
* The default value for the {@code maxIdle} configuration attribute.
* @see GenericObjectPool#getMaxIdle()
*/
public static final int DEFAULT_MAX_IDLE = 8;
/**
* The default value for the {@code minIdle} configuration attribute.
* @see GenericObjectPool#getMinIdle()
*/
public static final int DEFAULT_MIN_IDLE = 0;
private int maxTotal = DEFAULT_MAX_TOTAL;
private int maxIdle = DEFAULT_MAX_IDLE;
private int minIdle = DEFAULT_MIN_IDLE;
//......
}
pool基本參數(shù)
基本參數(shù)
lifo
GenericObjectPool 提供了后進(jìn)先出(LIFO)與先進(jìn)先出(FIFO)兩種行為模式的池。默認(rèn)為true，即當(dāng)池中有空閑可用的對象時，調(diào)用borrowObject方法會返回最近（后進(jìn)）的實例
fairness
當(dāng)從池中獲取資源或者將資源還回池中時 是否使用java.util.concurrent.locks.ReentrantLock.ReentrantLock 的公平鎖機制,默認(rèn)為false
數(shù)量控制參數(shù)
maxTotal
鏈接池中最大連接數(shù),默認(rèn)為8
maxIdle
鏈接池中最大空閑的連接數(shù),默認(rèn)也為8
minIdle
連接池中最少空閑的連接數(shù),默認(rèn)為0
超時參數(shù)
maxWaitMillis
當(dāng)連接池資源耗盡時，等待時間，超出則拋異常，默認(rèn)為-1即永不超時
blockWhenExhausted
當(dāng)這個值為true的時候，maxWaitMillis參數(shù)才能生效。為false的時候，當(dāng)連接池沒資源，則立馬拋異常。默認(rèn)為true
test參數(shù)
testOnCreate
默認(rèn)false，create的時候檢測是有有效，如果無效則從連接池中移除，并嘗試獲取繼續(xù)獲取
testOnBorrow
默認(rèn)false，borrow的時候檢測是有有效，如果無效則從連接池中移除，并嘗試獲取繼續(xù)獲取
testOnReturn
默認(rèn)false，return的時候檢測是有有效，如果無效則從連接池中移除，并嘗試獲取繼續(xù)獲取
testWhileIdle
默認(rèn)false，在evictor線程里頭，當(dāng)evictionPolicy.evict方法返回false時，而且testWhileIdle為true的時候則檢測是否有效，如果無效則移除
檢測參數(shù)
timeBetweenEvictionRunsMillis
空閑鏈接檢測線程檢測的周期，毫秒數(shù)。如果為負(fù)值，表示不運行檢測線程。默認(rèn)為-1.
commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java
public GenericObjectPool(PooledObjectFactory factory,
GenericObjectPoolConfig config) {
super(config, ONAME_BASE, config.getJmxNamePrefix());
if (factory == null) {
jmxUnregister(); // tidy up
throw new IllegalArgumentException("factory may not be null");
}
this.factory = factory;
idleObjects = new LinkedBlockingDeque>(config.getFairness());
setConfig(config);
startEvictor(getTimeBetweenEvictionRunsMillis());
}
commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/BaseGenericObjectPool.java
/**
* The idle object evictor {@link TimerTask}.
*
* @see GenericKeyedObjectPool#setTimeBetweenEvictionRunsMillis
*/
class Evictor extends TimerTask {
/**
* Run pool maintenance. Evict objects qualifying for eviction and then
* ensure that the minimum number of idle instances are available.
* Since the Timer that invokes Evictors is shared for all Pools but
* pools may exist in different class loaders, the Evictor ensures that
* any actions taken are under the class loader of the factory
* associated with the pool.
*/
@Override
public void run() {
ClassLoader savedClassLoader =
Thread.currentThread().getContextClassLoader();
try {
if (factoryClassLoader != null) {
// Set the class loader for the factory
ClassLoader cl = factoryClassLoader.get();
if (cl == null) {
// The pool has been dereferenced and the class loader
// GC"d. Cancel this timer so the pool can be GC"d as
// well.
cancel();
return;
}
Thread.currentThread().setContextClassLoader(cl);
}
// Evict from the pool
try {
evict();
} catch(Exception e) {
swallowException(e);
} catch(OutOfMemoryError oome) {
// Log problem but give evictor thread a chance to continue
// in case error is recoverable
oome.printStackTrace(System.err);
}
// Re-create idle instances.
try {
ensureMinIdle();
} catch (Exception e) {
swallowException(e);
}
} finally {
// Restore the previous CCL
Thread.currentThread().setContextClassLoader(savedClassLoader);
}
}
}
numTestsPerEvictionRun
在每次空閑連接回收器線程(如果有)運行時檢查的連接數(shù)量，默認(rèn)為3
private int getNumTests() {
int numTestsPerEvictionRun = getNumTestsPerEvictionRun();
if (numTestsPerEvictionRun >= 0) {
return Math.min(numTestsPerEvictionRun, idleObjects.size());
} else {
return (int) (Math.ceil(idleObjects.size() /
Math.abs((double) numTestsPerEvictionRun)));
}
}
minEvictableIdleTimeMillis
連接空閑的最小時間，達(dá)到此值后空閑連接將可能會被移除。默認(rèn)為1000L 60L 30L
softMinEvictableIdleTimeMillis
連接空閑的最小時間，達(dá)到此值后空閑鏈接將會被移除，且保留minIdle個空閑連接數(shù)。默認(rèn)為-1.
evictionPolicyClassName
evict策略的類名，默認(rèn)為org.apache.commons.pool2.impl.DefaultEvictionPolicy
public class DefaultEvictionPolicy implements EvictionPolicy {
@Override
public boolean evict(EvictionConfig config, PooledObject underTest,
int idleCount) {
if ((config.getIdleSoftEvictTime() < underTest.getIdleTimeMillis() &&
config.getMinIdle() < idleCount) ||
config.getIdleEvictTime() < underTest.getIdleTimeMillis()) {
return true;
}
return false;
}
}
這里就用到了上面提到的兩個參數(shù)
doc
Apache commons-pool對象池原理分析
GenericObjectPool 避免泄漏
apache-common-pool2（配置參數(shù)詳解，以及資源回收，從池中獲取資源，將資源返還給池 邏輯解析）
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